According to the state of the art, automatic transmissions, particularly for motor vehicles, are comprised of planetary gear sets, which are shifted using friction and/or shifting elements, such as clutches and brakes, and which are typically connected to a starting element, that is subject to a slip effect, and optionally provided with a converter lock-up clutch, for example a hydrodynamic torque converter or a fluid clutch.
Such a multi-speed automatic transmission, for example, is presented in DE 102 13 820 A1. In essence, it comprises an input shaft and an output shaft, which are located coaxially in relation to one another, a total of three planetary gear sets and six friction shifting elements. The transmission comprises two power paths for transmitting the torque from the input shaft to the output shaft. Two of the planetary gear sets form a shiftable primary gear set of the transmission in the form of a two-carrier four-shaft planetary gear designed, for example, as a Ravigneaux planetary gear set or as a Simpson planetary gear set. The output element of the primary gear set is connected to the output shaft of the transmission. The remaining one of the three planetary gear sets is configured as a simple planetary gear set and forms a non-shiftable front-mounted gear set, which is rigidly connected to the input shaft and produces a rotational speed on the output side, which is transmittable to the various input elements of the primary gear set. At any given time, by selectively locking two of the six friction shifting elements, configured as clutches and brakes, a total of eight forward gears can be engaged without range shifts, which is to say, that they can be shifted in such a way that during a change from one gear to the next higher or lower gear, only one of the previously engaged shifting elements is disengaged and a previously disengaged shifting element is engaged.
From DE 199 49 507 A1 by the applicant, a multi-speed transmission is also known, according to which, on the drive shaft two non-shiftable, front-mounted planetary gear sets are provided, which on the output side generate two rotational speeds which, in addition to the rotational speed of the input shaft, can be selectively switched by closing the control elements of two different input elements of a shiftable multi-component primary gear set, acting upon the output shaft in such a way that, for shifting from one gear to the next higher or next lower gear, of the two actuated control elements, only one control element must be engaged or disengaged. The primary gear set, in turn, is configured as a two-carrier four-shaft planetary gear set, the two planetary gear sets thereof being rigidly coupled to each other via two elements. When using five shifting elements, seven forward gears can be shifted into without range shifts, and when using six shifting elements, nine or ten forward gears can be shifted into.
Within the scope of DE 101 15 983 A1 by the applicant, a multi-speed transmission is described, comprising a drive shaft that is coupled with a front-mounted gear set, an output shaft that is connected with a rear-mounted gear set, and a maximum of seven shifting elements, through selective shifting at least eight forward gears can be shifted into without range shifting. The front-mounted gear set is formed by a shiftable or non-shiftable planetary gear set or of a maximum of two non-shiftable planetary gear sets that are coupled to one another. The rear-mounted gear set is a two-carrier four-shaft gear with two shiftable rear-mounted planetary gear sets and has four free shafts. The first free shaft of this two-carrier four-shaft transmission is connected with the first shifting element, the second free shaft with the second and third shifting elements, the third free shaft with the fourth and fifth shifting elements and the fourth free shaft is connected with the output shaft. According to the invention, a multi-speed transmission with a total of six shifting elements is proposed, which connects the third free shaft or the first free shaft of the rear-mounted gear set additionally with a sixth shifting element. For a multi-speed transmission with a total of seven shifting elements, it is proposed, according to the invention, that the third free shaft is additionally connected with a sixth shifting element and the first free shaft is additionally connected with a seventh shifting element.
A plurality of other multi-speed transmissions are known, for example, from DE 101 15 995 A1 by the applicant, wherein four shiftable planetary gear sets, which are coupled to one another, and six or seven frictionally engaged shifting elements are provided; the selective engagement of these elements transmits a rotational speed from an input shaft of the transmission to an output shaft of the transmission in such a way that nine or eleven forward gears and at least one reverse gear can be shifted into. Depending on the gearshift pattern, in each gear, two or three shifting elements are engaged, wherein during a shift from one gear to the next higher or next lower gear only one engaged shifting element is disengaged and a previously disengaged shifting element is engaged to prevent range shifting.
Furthermore, an 8-gear multi-speed transmission is known from DE 29 36 969 A1, comprising four coaxial simple planetary gear sets and eight friction shifting elements.
Another multi-speed automatic transmission is furthermore known from U.S. Pat. No. 4,683,776, comprising four single planetary gear sets and six friction shifting elements. All four planetary gear sets are configured as negative planetary gear sets in a simple planetary design. The first two planetary gear sets, viewed along the power flow, form a shiftable front-mounted gear set and are rigidly connected to one another via two coupling shafts, wherein the first coupling shaft of this front-mounted gear set rigidly connects the two sun gears thereof to one another as well as rigidly to the input shaft of the transmission, and the second coupling shaft of the front-mounted gear set rigidly connects the ring gear of the first planetary gear set with the planet carrier of the second planetary gear set and at the same time forms the output shaft of the front-mounted gear set. The two other elements of the front-mounted gear set—which is to say the planet carrier of the first planetary gear set and the ring gear of the second planetary gear set—can be fixed in place to the transmission housing via a separate brake. The third and fourth planetary gear sets form a shiftable primary gear set and are likewise rigidly connected to each other via two coupling shafts, wherein the first coupling shaft of this primary gear set rigidly connects the two sun gears thereof and can be connected to the input shaft of the transmission, and the second coupling shaft of the primary gear set rigidly connects the planet carrier of the third planetary gear set to the ring gear of the fourth planetary gear set and can likewise be connected to the input shaft and optionally can be fixed in place to the transmission housing via a brake. The ring gear of the third planetary gear set is a further input element of the primary gear set and is rigidly connected to the output shaft of the front-mounted gear set and can be fixed in place to the transmission housing via a further brake. The planet carrier of the fourth planetary gear set finally forms the output element of the primary gear set and is rigidly connected to the output shaft of the transmission. The transmission has a total of nine range shift-free shiftable forward gears and one reverse gear, which can be implemented by selectively engaging two of the six shifting elements, in pairs.
Furthermore, a 9-speed automatic transmission is known from U.S. Pat. No. 6,176,803 B1, comprising four shiftable simple planetary gear sets that are located coaxially in relation to one another and can also be coupled to one another, wherein this transmission has a strong resemblance to the automatic transmission according to U.S. Pat. No. 4,683,776, described above. Like in U.S. Pat. No. 4,683,776 a total of six friction shifting elements are provided, of which two are configured as multi-disk clutches and four as multi-disk brakes. Unlike in U.S. Pat. No. 4,683,776, the first of the four planetary gear sets, viewed along the power flow, is configured as a positive planetary gear set in a double planet design. As in U.S. Pat. No. 4,683,776, the remaining three planetary gear sets are configured as negative planetary gear sets in a simple planetary design. With the exception of coupling the sun gear of the second planetary gear set to the planet carrier of the first (positive) planetary gear set, the component-related coupling of the planetary gear sets among each other, to the two clutches, the input shaft, or the four brakes and to the output shaft are completely identical to U.S. Pat. No. 4,683,776. In principle, only the positive planetary gear set operates as a front-mounted gear set, whereby the remaining three planetary gear sets form the primary gear set of the transmission.
Similar multi-speed automatic transmissions with nine range shift-free shiftable forward gears are furthermore known from DE 4238025 A1, comprising four coaxial simple planetary gear sets and six or seven friction shifting elements (four multi-disk brakes and two or three multi-disk clutches). The first two planetary gear sets viewed, along the power flow, always form a shiftable front-mounted gear set, which is rigidly connected to the input shaft of the transmission and coupled via two coupling shafts, wherein one of the planetary gear sets is configured as a positive planetary gear set in double planet design and the other planetary gear set as a negative planetary gear set in a simple planet design. The remaining two planetary gear sets form a shiftable primary gear set identical to U.S. Pat. No. 4,683,776, configured as a two-carrier four-shaft planetary gear.
Automatic vehicle transmissions in planetary designs in general have previously been described in the state of the art on many occasions and undergo continuous developments and improvements. These transmissions should have, for example, a sufficient number of forward gears as well as one reverse gear and gear ratios that are excellently suited for motor vehicles, have a high overall ratio spread as well as favorable progressive ratios. Furthermore, they should allow a high starting gear ratio in the forward direction and include a direct gear and to be suitable for use in both passenger cars and commercial vehicles. In addition, these transmissions should have a low complexity, and in particular require a small number of shifting elements and avoid double-shifts when shifting sequentially, so that only one shifting element is engaged when shifting between defined gear groups.